API 5CT Tubing Pipe

Tubing Versus Casing

Casing is the permanent pipe cemented into the wellbore to maintain the hole and isolate formations; it stays in the well for the life of the field. Tubing is the smaller diameter pipe run inside the casing to conduct produced fluids to surface, and it is designed to be pulled and replaced. Because tubing hangs in tension from the wellhead, often in a long string, joint tensile strength and connection seal integrity under cyclic load dominate the design. Tubing is also exposed to the produced fluid on the inside, so corrosion and erosion resistance matter more than they do for casing, and it often carries the artificial lift equipment. Tubing is normally seamless and is available from about 1.05 inch up to 4-1/2 inch.

NUE, EUE and Premium Connections

NUE stands for non-upset end. The pipe body wall thickness is continuous through the threaded section, so the connection is weaker than the pipe body and the joint strength is limited to roughly 60 to 70 percent of body strength. It is used for shallow, low load applications. EUE stands for external upset end, where the pipe end is thickened before threading so the connection can be made stronger than the pipe body under tension. EUE is the standard connection for production tubing and is what most artificial lift equipment is designed to mate with. Premium connections provide a gas-tight metal-to-metal seal and a torque shoulder, giving reliable sealing under combined tension, pressure and bending, and are specified for gas wells, HPHT wells, deviated wells and any application where leak integrity is critical.